In this work the authors review various definitions of acids and bases. Furthermore, the application of these theories to surface and adhesion science is discussed. It is clear that application of various acid-base theories may not always lead to consistent conclusions on the acid-base character of surfaces. Possible reasons for the inconsistency include the nature of the scale, the choice of reference points, and the use of either poor or inconsistent statistical procedures in addition to experimental difficulties. The present authors recommend a future careful study and comparison of the various acid-base theories when applied to surface and adhesion science. The limited studies already preformed suggest this activity would be worthwhile.